Hydraulic cylinder for grain augers

ABSTRACT

A grain elevator auger uses a hydraulic cylinder incorporating a checkvalve. This checkvalve enables the volume of hydraulic fluid required to raise the elevator to be reduced to that required to replace the extended piston rod, instead of the full volume of the cylinder. The necessary capacity of the tractor hydraulic system reservoirs which are used to raise the elevators are similarly lessened. The checkvalve prevents hydraulic pressure retracting the piston, pressure is equalized on both sides of the cylinder piston, which then retracts slowly under the weight of the elevator, rather than rapidly under hydraulic pressure.

This invention relates to a single acting hydraulic cylinder forhydraulic lift systems for grain augers. A checkvalve is incorporatedinto a double acting hydraulic cylinder, which allows it to provideforce in one direction only.

Although the invention is described and referred to specifically as itrelates to specific structures of hydraulic cylinders, used in specificlifting systems for grain augers, it will be understood that theprinciples of this invention are equally applicable to similarstructures and accordingly, it will be understood that the invention isnot limited to such structures.

BACKGROUND OF INVENTION

Grain augers are used primarily to load grain into storage bins, and aretypically powered by the PTO (power take off) of a tractor. Thehydraulic lifting system of the grain auger is similarly powered by thehydraulic system of the tractor. Basically the auger is transported on acarriage usually consisting of one or more commonly two frames each oftwo legs, one frame being pivotally mounted on the other, which issupported by the axle of the carriage. When one frame is used it ispivotally mounted on the auger with a hydraulic cylinder pivotallymounted forward of the frame between the frame and the auger, byextending the cylinder the angle between frame and the forward portionof the auger is increased elevating the auger. When two frames are usedseveral arrangements are available. One version has one frame fixedlyand pivotally mounted on the auger, the other frame is slidably andpivotally mounted on the auger. By altering the distance between thefixed and slidable mountings the angle of the auger and its height canbe adjusted. Cables connect the slidable mounting to one or morehydraulic cylinders, and movement of the piston of the cylinder is usedto move the slidable mounting and thus change angle and height of thegrain auger. In this system the cylinder(s) or rather the associatedpiston(s) are extended to shorten the distance between the mountings.Other versions comprise the rear frame fixedly and pivotally mounted onthe auger, with the front frame pivotally and fixedly mounted on theauger and on the rear frame, and an intervening pivot in the frontframe, joining the upper front frame and the lower front frame. Ahydraulic cylinder or cylinders are pivotally mounted either between theauger and the upper front frame, or between the upper and lower frontframes, so that extension of the cylinder effectively straightens andlengthens the front frame as a whole elevating the auger.

PRIOR ART

Checkvalves of various types are known in association with hydrauliccylinders. U.S. Pat. No. 2,880,707, issued Apr. 7, 1959, to McCarthyteaches a dual cylinder sequential extension-retraction system with twoway checkvalves. U.S. Pat. No. 3,147,671 issued Sep. 8, 1964, to Geyerteaches a one way checkvalve to reduce compressive tension on a hollowpiston rod in a hydraulic cylinder for aircraft. U.S. Pat. No. 3,394,634issued Jul. 30, 1968, to Pfundt teaches a one way checkvalve to relieveexcess pressure during retraction. U.S. Pat. No. 3,476,016 issued Nov.4, 1969, to Dixon teaches a double cylinder system using one waycheckvalves, when the valves are open the pressure is equalized, butforce is not due to the piston rods; when the valves are closed equalpressure is exerted on both pistons, which thus have coordinatedmovement. U.S. Pat. No. 3,552,546 issued Jan. 5, 1971, to Rath anextendible retractable belt conveyor using hydraulic cylinders to extendlegs and the conveyor itself. U.S. Pat. No. 4,206,839 issued Jun. 10,1980, and U.S. Pat. No. 4,367,814 issued Jan. 11, 1983 to Young teachesa grain auger raised and lowered by cables and a hydraulically operatedwinch. U.S. Pat. No. 4,359,207 issued Nov. 16, 1992, to Maryonovich etal., teaches a winch cable system for raising a grain auger and asecondary safety cable system in case of failure.

The previous system used by applicant worked as follows, one or morehydraulic cylinders are connected on the piston side to the tractorhydraulic system and vented on the rod side. To extend the cylinderhydraulic fluid is pumped into the piston side, pushing the pistonupward until the cylinder is filled with hydraulic fluid and the airinitially on the rod side vented through the air vent. To lower thepiston the hydraulic pressure is released and the weight of the augerpushes the piston downward forcing hydraulic fluid from the cylinder.Under this system the hydraulic system of the tractor stores all thehydraulic fluid pumped during operation into the cylinder(s). Thetractor hydraulic system must contain enough hydraulic fluid to fill thecylinder(s), which prevents many tractors with smaller hydraulic fluidreservoirs from operating grain augers especially those with largerhydraulic cylinders. There is thus a need to reduce the volume ofhydraulic fluid required from the tractor reservoir to operate thesystem, so that tractors with smaller reservoirs can be used.

It is a principal object of the invention to reduce the volume ofhydraulic fluid, especially tractor hydraulic fluid required to operatea long single acting hydraulic cylinder, or cylinders. It is a furtherprincipal object of the invention to reduce the volume of hydraulicfluid, especially tractor hydraulic fluid, required to operate a longsingle acting hydraulic cylinder, or cylinders for grain augers. It is afurther principal object of the invention to provide an internalcheckvalve to achieve these ends. It is a further principal object toprovide an internal checkvalve to prevent tampering by those unfamiliarwith the design. It is a further principal object to provide an internalcheckvalve to reduce the chance of incorrect assembly. Other objectswill be apparent to those skilled in the art from the followingspecification, accompanying drawings and appended claims.

DESCRIPTION OF THE INVENTION

In one broad aspect the invention is directed to an improved heightadjustable elevator means, which has elongated conveyor means to conveymaterial and carriage means to support the conveyor means. The carriagemeans has front and rear frame members pivotally attached togetheradjacent their bases, and pivotally attached at their upper ends to theconveyor means. The upper ends of the front and rear frame members aremovable toward and away from each other. There are flexible cable meansattached at one end to one frame member adjacent the upper end thereofto draw the upper ends of the frame members toward each other to raisethe conveyor means. Also it allows the upper ends of the frame membersto move away from each other to lower the conveyor means. The flexiblecable means is attached at the other end to hydraulic cylinder meanshaving head and rod ends, and reciprocable piston means havingassociated piston rod means and operatively associated hydraulic linemeans attachable to vehicle hydraulic system means. The improvementprovides piston means including checkvalve means preventing flow throughthe piston means from head side to rod side allowing head side hydraulicpressure to extend the cylinder, and allowing flow from rod side, whichis full of hydraulic fluid, to head side preventing rod side hydraulicpressure retracting the cylinder, whereby the extra volume of hydraulicfluid necessary to extend the cylinder approximates that of the pistonrod means. Preferably the carriage means includes a traversing framemember and a fixed frame member. The lower end of the traversing framemember is pivotally attached to the lower end of the fixed frame member,and the upper end of the fixed frame member is fixedly pivotallyattached to the conveyor means, while the upper end of the traversingframe member is pivotally attached to the conveyor means inlongitudinally movable supporting contact. Preferably the traversingframe member comprises lower frame means and pivotally attached shoemeans slidably mounted in longitudinal track means on the conveyormeans, and the flexible cable means is attached to the shoe means.Alternatively the traversing frame member comprises lower frame means,lift assist means, and shoe means slidably mounted in longitudinal trackmeans on the conveyor means, the lift assist means is pivotally attachedto the shoe means and independently pivotally attached to the lowerframe means, while the flexible cable means is attached to the liftassist means. Conveniently there are two flexible cable means attachedat one end to one end of the frame member, and each flexible cable meansis attached at the other end to separate hydraulic cylinder means.

In another broad aspect the invention is directed to an improvedhydraulic cylinder means having head and rod ends, and reciprocablepiston means having associated piston rod means and operativelyassociated hydraulic line means attachable to vehicle hydraulic systemmeans. The improvement provides the piston means including checkvalvemeans preventing flow through the piston means from head side to rodside allowing head side hydraulic pressure to extend the cylinder, andallowing flow from rod side to head side, which prevents rod sidehydraulic pressure alone retracting the cylinder, whereby the extravolume of hydraulic fluid necessary to extend the cylinder approximatesthat of the piston rod means. Preferably the checkvalve means is springbiased one way checkvalve means.

Desirably these hydraulic cylinder means are incorporated into heightadjustable elevator means having elongated conveyor means to conveymaterial and carriage means to support the elevator means having a framemember pivotally attached at its upper end to the conveyor means. Oneend of hydraulic cylinder means is attached to the portion of theconveyor means in front of the paired frame members, and the other endis operatively associated with the frame member spaced apart from theconveyor means, so that when the hydraulic cylinder means is extendedthe angle between the front portion of the conveyor means and the frontside of the frame members is increased raising the conveyor means.Alternatively the carriage means includes front frame and rear framemembers pivotally attached at their upper ends to the conveyor means,where the front frame member has pivotally interconnected upper andlower frame members forming a forward acute angle. The upper front framemember has attached cradle means to receive one end of the hydrauliccylinder. The other end is operatively associated with the front end ofthe conveyor means so that when the hydraulic cylinder means is extendedthe angle between the front portion of the conveyor means and the upperfront frame member is increased raising the conveyor means. A thirdversion has the carriage means including front frame and rear framemembers pivotally attached at their upper ends to the conveyor means,where the front frame member has pivotally interconnected upper andlower frame members forming a forward acute angle. The hydrauliccylinder is however has one end attached to the upper front frame memberand the other attached to the front frame member, so that when thehydraulic cylinder means is extended the forward acute angle between theupper and lower front frame members is increased raising the conveyormeans. A fourth variation has the front frame member having pivotallyinterconnected upper and lower frame members forming a rearward acuteangle. Here the hydraulic cylinder means has one end attached to theupper front frame member and the other attached to the lower front framemember, so that when the hydraulic cylinder means is extended therearward acute angle between the upper and lower front frame members isincreased raising the conveyor means. When there are front and rearframe members these are pivotally attached at their lower ends to eachother. Basically powered lift means is provided for a height adjustableelevator means having elongated conveyor means to convey material andcarriage means to support the elevator means having at least one framemember pivotally attached at its upper end to the conveyor means, toraise one end of the elongated conveyor means, which includes thehydraulic cylinder means of the invention. Although the hydrauliccylinders as currently mounted in this broad aspect generally have theirpistons extending downward, this is not necessary for the practice ofthis aspect of the invention. The cylinders may be mounted to extend thepistons upward without affecting the practice of the invention, as thoseskilled in the art would realize.

In another broad aspect the invention is directed to a height adjustableelevator means having elongated conveyor means to convey material andcarriage means to support the conveyor means having front and rear framemembers pivotally attached together adjacent their bases, and pivotallyattached at their upper ends to the conveyor means. The front framemember has lower frame means and pivotally attached shoe means slidablymounted in longitudinal track means on the front portion of the conveyormeans. The upper end of the rear frame member is fixedly pivotallymounted on the rear portion of the conveyor means. There are flexiblecable means attached at one end to the upper end of the front framemember to draw it toward the rear frame member to raise the conveyormeans and also to allow the upper ends of the frame member to move awayfrom each other to lower the conveyor means. The flexible cable means isattached at the other end to hydraulic cylinder means having head androd ends, and reciprocable piston means having associated piston rodmeans and operatively associated hydraulic line means attachable tovehicle hydraulic system means. The hydraulic cylinder means has frontsheave means attached to the piston rod means and rear sheave meansadjacent the head end of the hydraulic cylinder means. The flexiblecable means passes from upper end of the front frame member around therear sheave means then around the front sheave means to anchor meansrearward of the hydraulic cylinder means, whereby extension of thecylinder piston means draws the front frame member toward the rear framemember. The improvement provides piston means including checkvalve meanswhich prevent flow through the piston means from head side to rod sideallowing head side hydraulic pressure to extend the cylinder, andallowing flow from rod side to head side preventing rod side hydraulicpressure retracting the cylinder, whereby the extra volume of hydraulicfluid necessary to extend the cylinder approximates that of the pistonrod means. The front frame member may comprise lower frame means, liftassist means, and shoe means slidably mounted in longitudinal trackmeans on the conveyor means, where the lift assist means is pivotallyattached to the shoe means and independently pivotally attached to thelower frame means and the flexible cable means is attached to the liftassist means. Preferably each sheave means comprises a plurality ofsheaves, more preferably triple. Preferably there are two flexible cablemeans attached at one end to upper end of the front frame member andeach the flexible cable means is attached at the other end to separatehydraulic cylinder means.

In another broad aspect the invention is directed to an improved heightadjustable elongated tube means having carriage means to support thetube means. The carriage means has front and rear frame memberspivotally attached together adjacent their bases, and pivotally attachedat their upper ends to the tube means. The front frame member has lowerframe means and pivotally attached shoe means slidably mounted inlongitudinal track means on the front portion of the tube means. Theupper end of the rear frame member is fixedly pivotally mounted on therear portion of the tube means. Flexible cable means are attached at oneend to the upper end of the front frame member to draw it toward therear frame member to raise the tube means and also to allow the upperends of the frame members to move away from each other to lower the tubemeans. The flexible cable means are attached at the other end tohydraulic cylinder means having head and rod ends, and reciprocablepiston means having associated piston rod means and operativelyassociated hydraulic line means attachable to vehicle hydraulic systemmeans. The hydraulic cylinder means have front triple sheave meansattached to the piston rod means and rear triple sheave means adjacentthe head end of the hydraulic cylinder means. The flexible cable meanspasses from the upper end of the front frame member around the rearsheave means then around the front sheave means to anchor means rearwardof the hydraulic cylinder means, whereby extension of the cylinderpiston means draws the front frame member toward the rear frame member.The improvement provides the piston means including checkvalve means,the checkvalve means preventing flow through the piston means from headside to rod side allowing head side hydraulic pressure to extend thecylinder, and allowing flow from rod side to head side preventing rodside hydraulic pressure retracting the cylinder, whereby the extravolume of hydraulic fluid necessary to extend the cylinder approximatesthat of the piston rod means. The front frame member may comprise lowerframe means, lift assist means, and shoe means slidably mounted inlongitudinal track means on the tube means. The lift assist means ispivotally attached to the shoe means and independently pivotallyattached to the lower frame means and the flexible cable means isattached to the lift assist means. Alternatively the front frame membermay comprise lower frame means and pivotally attached shoe meansslidably mounted in longitudinal track means on the tube means, whilethe flexible cable means is attached to the shoe means. Preferably eachsheave means comprises a plurality of sheaves, preferably triple.Preferably there are two flexible cable means attached at one end to thefront frame member and each flexible cable means is attached at theother end to separate hydraulic cylinder means.

To raise the auger tube, hydraulic pressure is applied to the head endof the cylinder and the piston forced rodward, typically a hydraulicpressure of 800 to 1600 psi is applied. This raises the auger tube andholds it in position during use. Generally the hydraulic pressure isremoved to lower the auger, whereupon gravity pushes down the auger tubeand retracts the piston. Should hydraulic pressure be reversed, theinternal checkvalve equalizes the pressure on either side of thecylinder, leaving a slight rodward force due to the hydraulic pressureapplied by the fluid opposite the piston rod. The weight of the augertube however retracts the piston.

The checkvalve inside the cylinder prevents hydraulic pressure beingapplied the wrong way, also it brakes the auger on lowering, if thepiston moves too fast the head side pressure will close the checkvalveand slow the piston. If hydraulic pressure is applied to the rod side ofthe cylinder the fluid will flow through the checkvalve and equalize thepressure. The internal checkvalve prevents tampering and/or erroneousassembly or replacement of the checkvalve, which would be easier with anexternal checkvalve.

As those skilled in the art appreciate considerable variation in augerand hydraulic cylinder size are possible, within the limits of theinvention. While typically the auger tubes range from about 8 to 13inches in diameter and about 50 to about 70 feet in length and thecylinders are about 4 inches in diameter, as those skilled in the artwould appreciate, greater and lesser values may be used.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side elevational part sectional view of anembodiment of the invention.

FIG. 2 is a schematic perspective front view of another embodiment.

FIG. 3 is a detailed sectional view of the embodiment of FIG. 1.

FIG. 4 is a detailed sectional view of the embodiment of FIG. 3.

FIGS. 5 to 8 are schematic side elevational views of further embodimentsof the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention is now illustrated by reference to the preferredembodiments thereof. Numeral 10 indicates an elevatable grain auger, asshown it in raised position, having elongated tube 12 containing theauger driven through gearbox 14 by tractor PTO (power take off) notshown. In FIGS. 1 and 2, tube 12 is carried by carriage 16 which haspaired from front legs 18, paired rear legs 20, and wheels 22. Frontlegs 18 are connected to roller trackshoe 24, either through lift assist26 (FIG. 1) or directly (FIG. 2). Trackshoe 24 is slidably mounted intrack or slide 30. Single cable 32 (FIG. 1) is connected to lift assist26 (FIG. 1), and passes around rear triple pulley 34 and front triplepulley 36, three times before attachment to anchor 38. Front triplepulley 36 is mounted on piston rod 40 of piston 42 of hydraulic cylinder44. Piston 42 has therein checkvalve 46, allowing flow from rod to headbut not the reverse flow from head to rod. Cylinder 44 has rod port 48and head port 50, connected during use to tractor 52's hydraulic systemby hydraulic lines 54 and 56. Carriage 16 is pivoted to trackshoe 24 attrackshoe pivot 58, to tube 12 at tube pivot 60, and to itself at framepivot 62, optionally front legs 18 may be attached to lift assist 26 atlift assist pivot 64. A double cable system is shown in FIG. 2, wherecables 132 and 134 are controlled by paired cylinders 144 and 146.

In FIG. 5, tube 12 is carried by carriage 16 which has paired legs 118,and wheels 22. Legs 118 are pivoted to tube 12 at rear tube pivot 160,cylinder(s) 144 pivot by piston rod 140 at rod end to legs 118 by legpivot 162, and at head end to tube 12 by front tube pivot 158. In FIG.6, tube 12 is carried by carriage 16 which has paired front legs 18,paired rear legs 20, and wheels 22. Rear legs 20 pivot on tube 12 bytube pivot 60. Front legs 18 are connected to lever arms 126, pivoted totube 12 by tube pivot 166, and front legs 18 by frame pivot 262. Supportarms 128 and 130 join at arm pivot 164. Cylinder 144 is pivoted at headend by tube pivot 158 and at rod end by arm pivot 164. In FIG. 7, tube12 is carried by carriage 16 which has paired front legs 18, paired rearlegs 20, and wheels 22. Rear legs 20 pivot on tube 12 by tube pivot 60.Front legs 18 are connected to lever arms 126, pivoted to tube 12 bytube pivot 166, and front legs 18 by frame pivot 262. Cylinder 144 ispivoted by at head end lever arm pivot 264, and at rod end by front legpivot 266. In FIG. 8, tube 12 is carried by carriage 16 which has pairedfront legs 18, paired rear legs 20, and wheels 22. Rear legs 20 pivot ontube 12 by tube pivot 60. Front legs 18 are connected to lever arms 126,pivoted to tube 12 by tube pivot 166, and front legs 18 by frame pivot262. Cylinder 144 is pivoted at head end by lever arm pivot 264, and atrod end by front leg pivot 266.

In use the head side and the rod side of the cylinder and bothconnecting lines are full of hydraulic fluid, when connected to tractor52. The fluid is pumped up line 56 to the head end of cylinder 44, 144or 146, urging checkvalve 46 closed and piston 42 extended, whichcontinues until the piston is fully extended. In FIG. 1 cable 32 istautened and shortened reducing the angle between legs 18 and 20, andelevating tube 12. In FIG. 2, cables 132 and 134 are also tautened andshortened, narrowing the angle between legs 18 and 20 and elevating tube12. In FIGS. 5 to 8, cylinders 144 are extended, either raising tube 12directly (FIG. 5) or straightening the leg 18 and lever arm 126 (FIGS. 6to 8) and thus raising tube 12 directly. When fluid flow is stoppedcheckvalve 46 remains closed due to downward pressure of auger tube 12.When fluid flow is reversed checkvalve 46 may open as necessaryequalizing pressure on either side of piston 42, preventing undesirablerod side pressure within hydraulic cylinder 44. The retraction of pistonrod 40 occurs solely under the weight of the auger. An advantage of theinvention is that the tractor hydraulic system only needs to supply thefluid necessary to displace the piston rod 40, rather than fill cylinder44 as formerly. A 56 inch stroke, 4 inch diameter cylinder with a 13/4inch diameter piston rod requires about 2.21 liters of hydraulic fluidunder the new system, as opposed to 11.53 liters under the old. When thedual cylinder system is used, 4.42 liters are required rather than 23.06liters. This means tractors with smaller hydraulic fluid reservoirs canbe used with grain augers of the invention. Also the tractor hydraulicreservoir remains relatively full to allow operating other equipmentwithout first needing to adjust the hydraulic fluid level in thereservoir.

Although the hydraulic cylinders as illustrated in FIGS. 5 to 8 havetheir pistons extending downward, this is not necessary for the practiceof these embodiments of the invention. The cylinders may be mounted toextend the pistons upward without affecting the practice of theseembodiments of the invention, as those skilled in the art will realize.

As those skilled in the art would realize these preferred describeddetails and materials and components can be subjected to substantialvariation, modification, change, alteration, and substitution withoutaffecting or modifying the function of the described embodiments.

Although embodiments of the invention have been described above, it isnot limited thereto, and it will be apparent to persons skilled in theart that numerous modifications and variations form part of the presentinvention insofar as they do not depart from the spirit, nature andscope of the claimed and described invention.

I claim:
 1. In a height adjustable elevator having an elongated conveyorfor material and a carriage to support said elevator having front andrear frame members pivotally attached together adjacent their bases, andpivotally attached at their upper ends to said conveyor,said upper endsof said front and rear frame members being movable toward and away fromeach other at least one flexible cable attached at one end to one saidframe member adjacent the upper end thereof to draw said upper ends ofsaid frame members toward each other to raise said conveyor and to allowsaid upper ends of said frame members to move away from each other tolower said conveyor, said flexible cable being attached at said otherend to a hydraulic cylinder having head and rod ends, and a reciprocablepiston having associated piston rod and operatively associated hydrauliclines attachable to the hydraulic system of a vehicle the improvementcomprising said piston including at least one checkvalve preventing flowthrough said piston from head side to rod side allowing head sidehydraulic pressure to extend said cylinder, and allowing flow from rodside to head side preventing rod side hydraulic pressure retracting saidcylinder, whereby the extra volume of hydraulic fluid necessary toextend said cylinder approximates that of the piston rod.
 2. Elevator ofclaim 1, wherein said carriage includes a traversing frame member and afixed frame member, the lower end of said traversing frame member beingpivotally attached to the lower end of said fixed frame member, saidupper end of said fixed frame member being fixedly pivotally attached tosaid conveyor said upper end of said traversing frame member beingpivotally attached to said conveyor in longitudinally movable supportingcontact.
 3. Elevator of claim 2, wherein said traversing frame membercomprises a lower frame member and a pivotally attached shoe slidablymounted in a longitudinal track on said conveyor, and said flexiblecable is attached to said shoe.
 4. Elevator of claim 2, wherein saidtraversing frame member comprises a lower frame member, a lift assistmember, and a shoe slidably mounted in a longitudinal track on saidconveyor, said lift assist member being pivotally attached to said shoeand independently pivotally attached to said lower frame member and saidflexible cable is attached to said lift assist member.
 5. Elevator ofclaim 1, wherein there are two said flexible cables attached at one endto one said frame member, and each said flexible cables is attached atthe other end to separate hydraulic cylinders.
 6. Elevator of claim 3,wherein said traversing frame member is at the front of said conveyerand said fixed frame member is at the rear of said conveyer and saidlongitudinal track is on the front portion of said conveyor,saidhydraulic cylinder having a front sheave attached to said piston rod anda rear sheave adjacent said head end of said hydraulic cylinder, saidflexible cable passing from said upper end of said front frame memberaround said rear sheave then around said front sheave to an anchorrearward of said hydraulic cylinder, whereby extension of said cylinderpiston draws said front frame member toward said rear frame member. 7.Elevator of claim 6, wherein each said sheave is multiple.
 8. Elevatorof claim 6, wherein said front frame member comprises a lower framemember, a lift assist member, and a shoe slidably mounted in alongitudinal track on said conveyor, said lift assist member beingpivotally attached to said shoe and independently pivotally attached tosaid lower frame member and said flexible cable is attached to said liftassist member.
 9. Elevator of claim 8, wherein each said sheave ismultiple.
 10. Elevator of claim 6, wherein there are two said flexiblecable attached at one end to said front frame member and each saidflexible cable is attached at the other end to separate hydrauliccylinder.
 11. In a height adjustable elongated tube having a carriage tosupport said tube, said carriage having front and rear frame memberspivotally attached together adjacent their bases, and pivotally attachedat their upper ends to said tube,said front frame member having a lowerframe member and a pivotally attached shoe slidably mounted in alongitudinal track on the front portion of said tube, said upper end ofsaid rear frame member being fixedly pivotally mounted on the rearportion of said tube, at least one flexible cable attach ed at one endto said upper end of said front frame member to draw said upper end ofsaid front frame member toward said rear frame member to raise said tubeand to allow said upper ends of said frame members to move away fromeach other to lower said tube, said flexible cable being attached atsaid other end to a hydraulic cylinder having head and rod ends, andreciprocable piston having associated piston rod and operativelyassociated hydraulic lines attachable to the hydraulic system of avehicle, said hydraulic cylinder having a front sheave attached to saidpiston rod and a rear sheave adjacent said head end of said hydrauliccylinder, said flexible cable passing from said upper end of said frontframe member around said rear sheave then around said front sheave to ananchor rearward of said hydraulic cylinder, whereby extension of saidcylinder piston draws said front frame member toward said rear framemember, the improvement comprising said piston including a checkvalvepreventing flow through said piston from head side to rod side allowinghead side hydraulic pressure to extend said cylinder, and allowing flowfrom rod side to head side preventing rod side hydraulic pressureretracting said cylinder, whereby the extra volume of hydraulic fluidnecessary to extend said cylinder approximates that of the piston rod.12. Tube of claim 11, wherein said front frame member comprises a lowerframe member, a lift assist member, and a shoe slidably mounted in alongitudinal track on said tube, said lift assist member being pivotallyattached to said shoe and independently pivotally attached to said lowerframe member and said flexible cable is attached to said lift assistmember.
 13. Tube of claim 11, wherein said flexible cable is attached tosaid shoe.
 14. Tube of claim 11, wherein there are two said flexiblecables attached at one end to said front frame member and each saidflexible cable is attached at the other end to separate hydrauliccylinders.
 15. A height adjustable elevator having an elongated conveyorto convey material and a carriage to support said elevator having atleast one frame member pivotally attached at its upper end to saidconveyor,and a powered lift to raise the front end of said elongatedconveyor said powered lift including at least one hydraulic cylinderhaving head and rod ends, and a reciprocable piston having associatedpiston rod and operatively associated hydraulic lines attachable to thehydraulic system of a vehicle the improvement comprising said pistonincluding checkvalve preventing flow through said piston from head sideto rod side allowing head side hydraulic pressure to extend saidcylinder, and allowing flow from rod side to head side preventing rodside hydraulic pressure alone retracting said cylinder, whereby theextra volume of hydraulic fluid necessary to extend said cylinderapproximates that of the piston rod.
 16. Elevator of claim 15 havingpaired frame members and said hydraulic cylinder has one end attached tothe portion of said conveyor in front of said paired frame members, andthe other end operatively associated with the front side of said pairedframe members spaced apart from said conveyor, so that when saidhydraulic cylinder is extended the angle between the front portion ofsaid conveyor and said front side of said frame members is increasedraising said conveyor.
 17. Elevator of claim 15 front frame and rearframe members pivotally attached at their upper ends to saidconveyor,said front and rear frame members being pivotally attached attheir lower ends to each other, said front frame member having pivotallyinterconnected upper and lower frame members forming a forward acuteangle, said upper front frame member having an attached cradle, saidhydraulic cylinder having one end attached to the portion of saidconveyor in front of said upper frame member, and the other endoperatively associated with the upper front frame cradle, so that whensaid hydraulic cylinder is extended the angle between the front portionof said conveyor and said upper front frame member is increased raisingsaid conveyor.
 18. Elevator of claim 15 having front frame and rearframe members pivotally attached at their upper ends to saidconveyor,said front and rear frame members being pivotally attached attheir lower ends to each other, said front frame member having pivotallyinterconnected upper and lower frame members forming a forward acuteangle, said hydraulic cylinder having one end attached to the upperfront frame member and the other end attached to said lower front framemember, so that when said hydraulic cylinder is extended the forwardacute angle between the upper and lower front frame members is increasedraising said conveyor.
 19. Elevator of claim 15 having front frame andrear frame members pivotally attached at their upper ends to saidconveyor,said front and rear frame members being pivotally attached attheir lower ends to each other, said front frame member having pivotallyinterconnected upper and lower frame members forming a rearward acuteangle, said upper front frame member having an attached cradle saidhydraulic cylinder having one end attached to the upper front framemember attached to said lower front frame member, so that when saidhydraulic cylinder is extended the rearward acute angle between theupper and lower front frame members is increased raising said conveyor.